Method for purifying 1,12-dodecanedioic acid

ABSTRACT

Crude 1,12-dodecanedioic acid obtained by oxidation of cyclododecanol and/or cyclododecanone by nitric acid is purified by dissolving the crude 1,12-dodecanedioic acid in an aqueous nitric acid solution containing 40 to 80 percent by weight of nitric acid at 85*-105*C, passing the resulting solution through a filter aid diatomaceous earth having particle sizes of 1-100 microns, cooling the resulting filtrate to 40*-90*C thereby to crystallize 1,12-dodecanedioic acid. The thus purified 1,12dodecanedioic acid has a good purity and a less susceptibility of discoloration appearing when dissolved in an alkali.

United States Patent ml Okada et al.

[54] METHOD FOR PURIFYING 1,12-

DODECANEDIOIC ACID [75] Inventors: Yoshihiko Okada; Takashi Matsubara,both of Nagoya, Japan [73] Assignee: Toagosei Chemical Industry Co.,

Ltd., Tokyo, Japan [22] Filed: April 6, 1971 [211 App]. No.: 131,817 v[3 0] Y Foreign Application Priority Data April 9, 1970 Japan ..45/29772[52] U.S. Cl ..260/537 P, 260/531 R [51] Int. Cl .4 ..C07c 51/42 [58]Field of Search ..260/537 P [56] References Cited UNITED STATES PATENTS3,637,832 l/1972 White et al ..260/537 P nil 3,714,244

I Jan. 30, 1973 3,366,680 l/l968 Minisciet al ..260/537 P PrimaryExaminer-Vivian Garner Att0rneyl(arl W. Flocks [5 7 1 ABSTRACT of l-lOOmicrons, cooling the resulting filtrate to- 4090C thereby to crystallize1,12-dodecanedioic acid. The thus purified 1,12-dodecanedioic acid has agood purity and a less susceptibility of discoloration appearing whendissolved in an alkali.

8 Claims, No Drawings METHOD FOR PURIFYING 1,12-DODECANEDIOIC ACID Thisinvention relates to a method for purifying 1,12- dodecanedioic acid,and more particularly to a method for purifying l,l2-dodecanedioic acidobtained by oxidation of cyclododecanol and/or cyclododecanone by nitricacid.

l,l2-Dodecanedioic acid is an industrially very useful material and isused as a raw material for polyamide and polyester. Particularly highpurity is required for 1,12-dodecanedioic acid, when used.

However, the l,l2-dodecanedioic acid (which will be hereinafter referredto as DDA) obtained by oxidation of cyclododecanol and/orcyclododecanone by nitric acid contains by-product dibasic acids having1 l or less carbon atoms and nitrogen-containing impurities, and thus,DDA having a good purity and a less susceptibility of discolorationappearing when dissolved in an alkali has not been heretofore readilyobtained. For example, the crude DDA crystals obtained by carrying outan oxidation reaction at 60C in the presence of a copper-ammoniummetavanadate catalyst using 60 percent nitric acid and separating theresulting product at 30C by filtration contains 5002,000 ppm (in termsof nitrogen, N ofsuch nitrogen-containing compounds as nitro and nitrosocompounds, nitrite esters, etc. and 2-3 percent of dibasic acids having11 or less carbon atoms, and is colored to yellow when dissolved in analkali (optical density: 2 or higher). These impurities and coloringcannot be removed almost at all by washing the crude DDA with water.

Heretofore, a recrystallization method using such an organic solvent astoluene, ethyl alcohol, polyethyleneglycol dialkylether, acetone oracetic acid has been proposed as the method for purifying the crude DDA,but such a method has not been utilized widely as an industrial scaleprocess, because of a higher DDA cost duet'o the use of the solvent,inevitable loss of DDA in the solvent by dissolution, the necessity forsolvent recovery and the necessity for several recrystallizations when ahigh purity DDA is to be obtained by mere recrystallization method, aswill be shown in the following example. For example, Japanese Pat.publication No. 23389/64 discloses an example that the nitrogen contentof crude DDA can be reduced from 1,400 ppm to 210 ppm byrecrystallization by ethyl acetate, and successively from 210 ppm to 150ppm by the second recrystallization by ethyl acetate. This example showsthat it is difficultto purify crude DDA by mere recrystallization by anorganic solvent.

On the other hand, French Pat. No. 1,392,568 discloses a method forseparating lower dibasic acids from crude DDA by treating the crude DDAwith boiling water, but even in that process, the separation efficiencyis not always satisfactory. For example, a crude DDA containing 98.6percent l,l2-dodecanedioic acid, 1 percent 1,1 l-un-decanedioic acid and0.2 percent l,l-decanedioic acid can be purified to a pure DDA having99.5 percent 1,12-dodecanedioic acid, 0.4 percent 1,1 l-un-decanedioicacid and a trace of 1,10- decanedioic acid by boiling water treatment.

Further, a recrystallization method by hot water under pressure wasproposed (Japanese Pat. publication No. 23389/64). However, these priorart methods are not so effective for removing the nitrogen-containingcompounds and separating lower dibasic acids.

An object of the present invention is to improve these disadvantagesinherent in these prior art methods and provide a method for obtainingDDA having a high purity and a less susceptibility of discolorationappearing when dissolved in an alkali in high yield.

The present inventors have found an unexpected fact that the crude DDAhas a considerably high solubility in an aqueous nitric acid solution,which cannot be expected in a water solvent system, the organicnitrogencontaining compounds contained in the crude DDA are very rapidlydecomposed to the compound having a good solubility under saiddissolution treatment in said aqueous nitric acid solution, and thelower dibasic acids having 11 or less carbon atoms have a considerablyhigh solubility in said aqueous nitric acid solution.

Further, the present inventors have found that when the DDA crystals areobtained by cooling and crystallizing the aqueous nitric acid solutionof crude DDA, the nitrogen-containing compounds and the by-product acidshaving 11 or less carbon atoms can be effectively separatedand removedtherefrom by properly selecting the separation temperature.

As a result of various studies on an improvement in discolorationappearing when the DDA is dissolved in an alkali, heat stability at ahigh temperature (for example, the degree of discoloration at 250C in anitrogen gas stream) and polymer qualities, particularly discolorationwhen used in the polyamide synthesis, on the basis of said findings, thepresent inventors have found that these properties can be improved veryremarkably by filtering the aqueous nitric acid solution of crude DDAthrough afilter aid having particle sizes of 1 to 100 microns in main,before the solution is cooled and crystallized, and have accomplishedthe present invention.

According to the result of the studies on a correlation' between thequality of the DDA and the quality of the polymer synthesized from theDDA, made by the present inventors, it has been found that the degree ofthe discoloration appearing when the DDA is dissolved in the alkali andthe degree of heat stability at a high temperature,for example, 250C arein a close relation to the degree of discoloration of the polyamide.

That is to say, to obtain a polyamide unsusceptible to thediscoloration, it is important to use DDA having a discoloration of 0.05or less when dissolved in an alkali and a heat stability of 500 or lessin terms of hazen color unit (in nitrogen gas stream at 250C for 2hours). In the present invention, these conditions can be satisfiedcompletely.

Various filter aids such as diatomaceous earth, active carbon, etc., arecommercially available, but the filter aid used in the present inventionis the so-called diatomaceous earth. For example, Celite 545, Celite535, Celite 503, HiFlo supercell, standard supercell, and Filter cell(each being trademark of Johns Manville Corp. USA for the diatomaceousearth) can be used i establishing a compact filter layer.

cally unsuitable. The diatomaceous earth having particle sizesof morethan 100 microns is not effective almost at all as a filter aid or alarger amount thereof must be used when fine materials are to befiltered off. Thus, the diatomaceous earth having particle sizes of morethan 100 microns is disadvantageous for an industrial practice. It ispreferable to use the diatomaceous earth by precoating it in advance,but it is possible to use it in a suspended state.

It is desirable that the filter aid used in the present invention canform a compact filter layer and a function of the so called absorbingagent is not so much 1 required. That is to say, it is desirable thatthe surface structure of the filter aid is in a form suitable for Thereasons why the diatomaceous earth is most suitable for attaining theobject of the present invention is not clear yet, but it seems that thediatomaceous earth has a special affinity towards the impurities, whichare causes for effecting discoloration and impairing the heat stability,when the diatomaceous earth is brought in contact with the aqueousnitric acid solution of thecrude DDA. This assumption would hold truefrom the fact that, for example, active carbon, which has been so farused frequently in adsorption and removal of the impurities, cannotattain the object of the present invention (see Comparative Example 4which follows), and it is clear that these impurities cannot be removedsimply byan adsorbingfunction.

The diatomaceous earth can be used in any amount, so long as thefiltration resistance is within an allowable range, and a very smallamount of filtering cakeean satisfy the desired duty. That is, it ispossible to treat the aqueous nitric acid solution in an amount 10,000to 100,000 times the amount of the diatomaceous earth used.

The aqueous nitric acid solution containing 40 to 80 percent by weightof nitric acid is used in the present invention, to dissolve thecrudeDDA. Preferably, the solution containing 50 to 70 percent by weightof'nitric acid is used. The solution containing less than 40 percent byweight of nitric acid is not enough to decompose the nitrogen-containingcompounds, and when the nitric acid concentration exceeds 80 percent,the yield of DDA is lowered. Said concentration of the aqueous nitricacid solution is defined by percent by weight under the heatingtreatment condition (HNO /HN H O).

0.5 to parts, preferably 1 to 3 parts by weight of nitric acid is usedper one part by weight of crude DDA. When the crude DDA is dissolved inthe aqueous nitric acid solution, it is preferable to dissolve it underheating. its optimum temperature depends upon the concentration of theaqueous nitric acid solution, but a temperature over 120C is notparticularly necessary. The heating temperature is above 70C, preferablyin a range of 85-l05C. The time required for the dissolution by heatingis 20 minutes to 2 hours, preferably 30 to 60 minutes.

When the crude DDA is dissolved in the aqueous nitric acid solution, aconsiderable amount of NO and NO, is generated, but NO and NO, can berecovered, for example, as nitric acid by absorbing them in water. Thus,the loss of nitric acid at the dissolution is very small.

The solution resulting from the dissolution by heating can be passedthrough the filter aid having particle sizes of l to 100 microns in mainat any temperature, so

long as the temperature can 'maintain DDA in a dissolved state. Forexample, the filtration can be carried out at 95C. Then, the filtrate iscooled to recrystallize DDA, and successively the deposited crystals areseparated from a mother liquorby filtration, whereby DDA crystals havinga high purity, a good heat stability and a less susceptibility ofdiscoloration by an alkali can be obtained with a recovery efficiencyof'97 percent or higher by mole.

The temperature for crystallizing the filtrate depends upon the amountof impurities, particularly l,ll-undecanedioic acid, containedin thecrude DDA and the concentration and the amount of the aqueous nitricacid solution to be used, but usually is in a range of 40-90C. Forexample, the optimum temperature is 80C when an aqueous 60 percentnitric' acid solution is used.

In the crystallization, the well-known continuous or batch-typecrystallizer can be usually used. The separation of crystals can becarried out by filtration or centrifugal separation, and the resultingmother liquor can be recycled to and reused in the oxidation system.

. According to the present invention, l,l2- dodecanedioic acid having ahigh purity, a good heat stability and a less susceptibility ofdiscoloration by an alkali can be readily obtained in high yield, asdescribed above, and the present invention is useful for obtaining theDDA crystals, particularly applicable to the synthesis of polyamide orpolyester.

Now, the present invention will be explained in detail, referring toExamples, Reference Example and Comparative Example. The results ofExamples and Comparative Examples are listed in the following Table 2.

REFERENCE EXAMPLE Into a 20-] stainless steel reactor provided with astirrer was placed a solution prepared by dissolving 29.92 g of copperpowders and 9.97 g of ammonium metavanadate in 24,934 g of anaqueous 60percent wt. nitric acid solution. To said solution was supplied asolution mixture prepared by dissolving 2,456.6 g of a mixtureconsisting of percent by weight of cyclododecanol and 5 percent byweight of cyclododecanone in 454.3 g of cyclododecanol by heating, whilekeeping a reaction temperature at 60C over a period of minutes. Afterthe completion of the supply, the temperature was elevated and kept at,

0.4 percent by weight, respectively, and water was 8.6

percent by weight. The crude DDA was dried at 95C for 2 hours in an airdrier, and, after drying, subjected to nitrogen analysis by Kjeldahlmethod. It was found i that thenitrogen content was 840.3 ppm.

EXAMPLE 1 200 g of the crude DDA (in a wet state) obtained in ReferenceExample was dissolved in 400 g of an aqueous 67 percent wt. nitric acidsolution under heating, and the resulting solution was kept at 95C for30 minutes with stirring. Then, the said nitric acid was passed througha filter precoated with 5 g of filter aid, Celite 545 having particlesizes of 12 to 40 p. (the particle sizes being represented by percent ata lower limit to 80 percent at an upper limit). Then, the filtrate wascooled down to 40C with stirring over a period of 120 minutes. The DDAdeposited as crystals was filtered and separated, and washed with l l ofhot water and dried at 95C for 2 hours with air, whereby 163 g ofcrystals was obtained. Recovery efficiency from the crude DDA was 97percent by mole. The analysis of DDA before and after the purificationis shown in Table 1.

whereby nylon 6-12 was obtained. The thus obtained polymer was purelywhite and had no discoloration, a relative viscosity of 1.75 (0.1 g ofnylon/25 cc of metacresol: C) and a molecular weight of 1.7 X 10(measured by an osmotic pressure method).

The results are shown in Table 2.

EXAMPLES 26 Treatment was carried out in the same manner as in Example1, except that the filter aids listed in Table 2 were used in place ofthe filter aid of Example 1. The results are shown in Table 2. Thecontent of by-product dibasic acid after the purification was almostequal to those of Example 1.

COMPARATIVE EXAMPLE Treatment was carried out in the same manner as inTABLE 1 Example 1, except that no filter aid was used. The Crude p fireSult 18 shown in Table 2. Nitrogen content 840.3 ppm 5 ppm I COMPARATIVE EXAMPLES 2-4 1,1 l-Undecanedioic id Content 2] l% o 20Treatment was carried out 111 the same manner as In ldg-d tan di 0 4 q 00 Example 1, except that filter aids other than gil g zi i 'z by Odiatomaceous earth were used. The results are shown alkali dissolutionin Table 2.

TABLE 2 lnrilivntion result Diseolorw lnrlicle size, p. tion by (10% nt.:1 lower nlkali lleat limit to S09; Nitrogen dissolution stability(,olor at an upper content optical (llazen of poly- Filtor aid limit)(p.p.|n.) density) t'OlOl unit) amide Example 1 -15 0. 025 300 WhiteExample 2. -17 0.030 300 Do. Emmple 3. I 3 40 0. 027 250 Do. Example 4lit-Flo Supereell 48 0.032 350 Do. Example 5. Standard Supcrcell -110.021) 200 Do. Example 6 Filter Cell 411 0. 026 2.50 Comparative Example1 No liltration 55 0.074 800 Brown. Comparative Example 2 411 0.060 600Grey. Com parativc Example 3. 43 0. 0511 700 Brown. Comparative Example4"... Granular active earho 40 0.048 600 Do.

1 Glass filter N0. 4 made by Sliibata Kngakn Kikai Kogyo K. K.. Japan.

2 or more H eat stability Note 1. 1 g of DDA is dissolved in cc of 1Nsodium hydroxide solution and a transmission (T percent) is measured ata wavelength of 370 millimicron and a cell of 10 mm. The transmission of1N sodium hydroxide solution is presumed to be 100, and thediscoloration by a1- kali dissolution is defined by the followingformula: Discoloration by alkali dissolution log 100/1) Note 2. 20 g ofDDA is placed in a colorimetric tube and melted in a nitrogen gas streamat 250C and its discoloration is measured after 2 hours. The value isshown in hazen color unit (.IlSK-4172).

Further, 700 g of the purified DDA obtained according to the same manneras in Example 1 was suspended in 700 g of water and heated to 6070C.Then, an aqueous solution of 50 percent by mole of hexamethylene-diaminewas added thereto drop by drop and the pH was kept to 7.5, whereby auniform aqueous solution of nylon salt was obtained.

1,500 g of said solution was fed to a 2-1 capacity stainless steelautoclave (SUS-32) and the autoclave atmosphere was replaced withnitrogen completely.-

Then, the temperature of the autoclave was elevated. When thetemperature of the autoclave was elevated to 70C, the autoclaveatmosphere was replaced again with the nitrogen, and the nitrogenpressure was increased to 10 kg/cm gage. Further, the autoclavetemperature was gradually elevated, kept at 220C for one hour, and thenelevated to 260C.

The autoclave pressure was returned to the atmospheric pressure overabout one and a half hour while keeping the temperature at 260C. Then,the nitrogen gas was passed through the autoclave for three hours, andthen the resulting polymer was cooled down to the room temperature in anitrogen gas stream,

What is claimed is:

l. A method for purifying crude 1,12-dodecanedioic acid obtained byoxidation of cyclododecanol or cyclododecanone or mixtures thereof bynitric acid, which comprises dissolving crude 1,12-dodecanedioic acid inan aqueous nitric acid solution containing 40 to percent by weight ofnitric acid at a temperature above 70C, passing the resulting solutionthrough a filter of diatomaceous earth having particle sizes of 1-100microns, cooling the resulting filtrate to 4090 C thereby to crystallize1,12-dodecanedioic acid.

2. A method according to claim 1, wherein said aqueous nitric acidsolution contains 50-70 percent by weight of nitric acid.

3. A method according to claim 1, wherein said resulting solution has atemperature of about 95C.

4. A method according to claim 1, wherein 0.5 to 10 parts by weight ofsaid nitric acid is used to dissolve one part by weight of said crude1,12-dodecanedioic acid.

5. A method according to claim 4, wherein the weight ratio of nitricacid to crude 1,12-dodecanedioic acid is l3:1.

6. A method according to claim 1, wherein the crude 1,12-dodecanedioicacid is dissolved in the aqueous nitric acid solution at -105C.

7. A method according to claim 6, wherein said aqueous nitric acidsolution contains about 60 percent by weight of nitric acid.

8. A method according to claim 7, wherein the filtrate is cooled to70-80C thereby to crystallize 1,12- dodecanedioic acid.

1. A method for purifying crude 1,12-dodecanedioic acid obtained byoxidation of cyclododecanol or cyclododecanone or mixtures thereof bynitric acid, which comprIses dissolving crude 1,12-dodecanedioic acid inan aqueous nitric acid solution containing 40 to 80 percent by weight ofnitric acid at a temperature above 70*C, passing the resulting solutionthrough a filter of diatomaceous earth having particle sizes of 1-100microns, cooling the resulting filtrate to 40*-90*C thereby tocrystallize 1,12-dodecanedioic acid.
 2. A method according to claim 1,wherein said aqueous nitric acid solution contains 50-70 percent byweight of nitric acid.
 3. A method according to claim 1, wherein saidresulting solution has a temperature of about 95*C.
 4. A methodaccording to claim 1, wherein 0.5 to 10 parts by weight of said nitricacid is used to dissolve one part by weight of said crude1,12-dodecanedioic acid.
 5. A method according to claim 4, wherein theweight ratio of nitric acid to crude 1,12-dodecanedioic acid is 1-3:1.6. A method according to claim 1, wherein the crude 1,12-dodecanedioicacid is dissolved in the aqueous nitric acid solution at 85*-105*C.
 7. Amethod according to claim 6, wherein said aqueous nitric acid solutioncontains about 60 percent by weight of nitric acid.